1. Field of the Invention
This invention relates to alternators of the type that are used in vehicles to provide electrical power for running accessories and charging batteries. More particularly, this invention relates to a high-efficiency hybrid alternator in which the rotating magnetic field is provided by a rotor having a permanent magnet portion and a wound field portion operating in combination.
2. Description of Related Art
The automotive industry has been attempting to increase the efficiency of motorized vehicles, both at idle and at running speeds. It is particularly important to increase efficiencies at idle because it has been determined that about one half of all the consumption of fuel takes place at idle. The alternator design most commonly found in vehicles has been used for approximately twenty-five to thirty years and is inexpensive to produce, but exhibits very low efficiency levels, as low as 40-50%. The problem is particularly acute at low RPMs where high excitation levels in the rotor winding are required to produce the desired voltage, leading to very low efficiency.
In conjunction with the desire for higher efficiency is the need to supply alternators that have larger electrical ratings because modern vehicles have many more motors and require much more electrical power. Moreover, fuel efficiency of vehicles is closely related to the weight of the vehicle and it is desirable to decrease the weight of the alternator so as to minimize the total vehicle weight. These objectives are achieved when the efficiency of the alternator is increased.
The increased power usage in vehicles has also led to an interest in using components that operate at higher voltages than the standard 12 volts presently used in automobiles. At the same time, it is foreseen that 12 volt power will be required in such vehicles in addition to the higher voltage.
It is known to provide dual voltage alternators by providing two windings on the stator. However, when a single winding is used on the rotor, it is difficult to properly regulate the two different voltage outputs as different levels of rotor excitation current may be required for the different circuits. Single and dual voltage alternators of the type represented by the present invention may also be used in various non-engine driven applications, such as wind or water driven applications, for the efficient generation of electrical power.
In view of the problems with the prior art, one object of the present invention is to provide an alternator which operates efficiently at low RPMs.
Another object of the invention is to provide an alternator which uses a permanent magnet assembly in the rotor to provide a rotating permanent magnetic field in combination with a rotating variable magnetic field generated by a rotor winding.
Still another object of the invention is to provide an alternator which weighs less than current alternators at the same output power or which produces a higher output at the same weight.
Yet another object of the present invention is to provide an efficient dual voltage alternator, preferably in which both voltages are well regulated under varying loads.